s,nopr.niscair.res.in/bitstream/123456789/52477/1/IJCA 16A(6) 519-520.pdfFormation rate of...
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COMMUNICA TlONS Kinetics & Mechanism of Halogenative Oligomerization of Mesityl Oxide by Chloramine-T: Evidence for a Novel Pathway in Aqueous Sulphuric Acid* TABLE 1- STABILITY CONSTANTS OF MIXED LIGAND COMPLEXES [Temp. = 25°; !1. = 0·1 (NaCIO.); pH = 4'0] System Stability constant Ref. ~Ni(en)~+ ~4Ni(cN)1- KfJi)~n. K,K2k3 K.' s, K, K2 K,K2 K121 ~112 2'40 X 10 13 2·54 X 10 30 1·50 X 10' 2·39 X 10 9 1'08 X 10- 7 1'37 X 10 7 1·05 X 10 3 1'42 X 10 10 1·37 X 10 7 4·29 X 10 15 7 8 9 This work do do do do do do Formation rate of tetracyanonickelate(II) - The rate of reaction was measured by monitoring the forma- tion of [Ni(CN)i-] with time spectrophotometrically at 267 nm (e = 1·16x 10 4 M-I em-I) and 285 nm (e = 4-63 X 10 3 M-I cnr+). Kinetic runs were carried out in the presence of large excess of cyanide under conditions described above. Excellent pseudo-first order: plots were obtained on plottion log (A -At) vs time (Fig. 1). A variable depen- dence of rate o~ [cyanide] was observed as in the case of aminocarboxylatesv". The slopes of these plots gave first order rate constant k3 and second order rate constant K 2 k 3 . Third order dependence was not seen in this case though the same has been re- ported for some aminocarboxylates--". Dissociation rate of tetracyanonickelate(II) in presence of excess ethylenediamine - The rate of reverse reaction was measured by observing the disappearance of Ni(CN)~- at 267 nm or 285 nm. The reverse reaction was forced in the presence of large excess of ethylenediamine. The reverse re- notion is first order in [Ni(CN)~-], first order In [ethylenediamine] and inverse first order in [cyanide]. The value of reverse rate constant k; (= K 4 I k_ 3 ) was calculated from inverse first order plots (not shown). Evaluation of stability constants of mixed inter- mediate complexes - The values of forward and reverse rate constants as determined above made it possible to evaluate the stability constants of intermediates of steps (1) and (2) as defined in Eqs. (6) and (8). These values and also the values of other constants that have been used in these calculations are given in Table 1. References 1. KUMAR, K. & NIGAM, P. C., Paper presented at Annual Convention of Chemists (India), 1977. 2. KL:MAR, K., NIGAM, P. C. & PANDEY, G. S., J. phys. cu»; (in press). 3. COO~!BS, L. C., MARGERUM, D. "V. & NIGAM, P. C., Tnorg, Chem., 9 (1970), 2081. 4. COOMBS, L. C. & MARGERUM, D. W., Inorg. Chem., 9 (1970), 1711. 5. MARGERUM, D. "V., BYDALEK, T. J. & DISHOP, J. J., J. Am. chem. Soc., 83 (1961), 1791. 6. PAGENKOPF, G. K., J. coord. Chem., 2 (1972), 129. 7. DAVIES, T., SINGER, S. S. & STAVELEY, L. A. K., J. chem, Soc. (Lond.), (1954), 2304. 8. CROUSE, "V. C. & MARGERUM, D. W., Inorg, cu-«, 7 (1968), 2239. 9. CAULLET, c.. Bull. Soc. cu«, s-: (1963), 688. S. VIVEKANANDAN, K. VENKATARAO & M. SANTAPPA Department of Physical Chemistry, University of Madras Guindy Campus, Madras 600025 and SP. SHANMUGANATHAN Department of Chemistry, Pachaiyappa's College Madras 600030 Received 26 April 1978; accepted 23 May 1978 The kinetics of the reaction between mesityl oxide and chloramine-T (CAT) in aqueous sulphuric acid in the presence of KHSO. has been studied. The results indicate a radical chain mechanism to be operative which is quite novel in CAT kinetics. C HLORAMINE-T (CAT) has estab!ished itself as an efficient and dependable OXidant and a versatile chlorinating agent in chemical analysis--' and in reaction kinetics=". Only simple products ha ve been noticed so far in its reaction with substratess", We report in this communi~ation .our kinetic evidence for a novel halogena tive oligo- merization of mesityl oxide (MO) by chloramir.e-T in aqueous (O'375M) sulphuric acid.. . In the presence of KHS0 4 , the r~actIO!l manifests a typical fractional order behaVIOur, i.e. a clean 1·5 order in [CAT] and a 0·5 order at low [MO] «O·OI5M) which changes to zero. order . ~md~r pseudo conditions (1:.15).. Thi~ is. qurte f"!luhar l,n free radical polymerization kinetics. Beslde~ th:s Michaelis-Menten type of behavic:~r, .the rea.ctIOn IS associated with very fast equilibria dunng the initial stages. This kinetic evidence fo~ co.mplex formation is supported by the large shifts m the A values for the reaction mixture when com- p~~~d to those of the reactants. A ne&ligible salt effect (fL: 0·477M to 0'777M; k at 40 : 0·219 to 0.2671\,1- 0 • 5 sec+) and a marginal increase in rate with increasing [H30+] (0·113M to 0'375M; ~ at 40°: 0·244 to O·320M-0.5 sec+) have been noticed. This beha viour indicates that the ionic mechanism postulated in reactions involvir,g. CA1 6 may r.ot.be operative under our kinetic conditions. The reaction is considerably faster in the absence of. added mineral acids suggesting <in altogether different mechanism. Initially added CI. has a marked influence on the rate which could be explained by its oxidation to Cl" that helps fz ster prop, gat ion of the chains. The overall activation energy is 64·7 kJ mol! (35-50°; k: 0·254 to O·958M-0.5 see-I). Mass law effect is not observed. Ir.stead, the rate increases slightly with increasing initially cdded p-toluenesulphonamide (PTS) which is one of the *Presented as a preliminary report at the All I.ndia seminar on Oxidation-reduction reactions held at the Univer- sity of Madras, January 1978 and with further results presented as a paper at the Chemistry symposium held at the lIT. Madras, March 1978. 519
Transcript of s,nopr.niscair.res.in/bitstream/123456789/52477/1/IJCA 16A(6) 519-520.pdfFormation rate of...
COMMUNICA TlONS
Kinetics & Mechanism of HalogenativeOligomerization of Mesityl Oxide by
Chloramine-T: Evidence for a Novel Pathwayin Aqueous Sulphuric Acid*
TABLE 1- STABILITY CONSTANTS OF MIXED LIGANDCOMPLEXES
[Temp. = 25°; !1. = 0·1 (NaCIO.); pH = 4'0]
System Stability constant Ref.
~Ni(en)~+~4Ni(cN)1-
KfJi)~n.K,K2k3K.' s,K,K2K,K2K121
~112
2'40 X 10132·54 X 1030
1·50 X 10'2·39 X 109
1'08 X 10-7
1'37 X 107
1·05 X 103
1'42 X 1010
1·37 X 107
4·29 X 1015
789
This workdodododododo
Formation rate of tetracyanonickelate(II) - The rateof reaction was measured by monitoring the forma-tion of [Ni(CN)i-] with time spectrophotometricallyat 267 nm (e = 1·16x 104M-I em-I) and 285 nm(e = 4-63 X 103M-I cnr+). Kinetic runs were carriedout in the presence of large excess of cyanide underconditions described above.
Excellent pseudo-first order: plots were obtained onplottion log (A -At) vs time (Fig. 1). A variable depen-dence of rate o~ [cyanide] was observed as in the caseof aminocarboxylatesv". The slopes of these plotsgave first order rate constant k3 and second orderrate constant K2k3. Third order dependence wasnot seen in this case though the same has been re-ported for some aminocarboxylates--".
Dissociation rate of tetracyanonickelate(II) inpresence of excess ethylenediamine - The rate ofreverse reaction was measured by observing thedisappearance of Ni(CN)~- at 267 nm or 285 nm.The reverse reaction was forced in the presence oflarge excess of ethylenediamine. The reverse re-notion is first order in [Ni(CN)~-], first orderIn [ethylenediamine] and inverse first order in[cyanide]. The value of reverse rate constant k;(= K4Ik_3) was calculated from inverse first orderplots (not shown).
Evaluation of stability constants of mixed inter-mediate complexes - The values of forward andreverse rate constants as determined above madeit possible to evaluate the stability constants ofintermediates of steps (1) and (2) as defined inEqs. (6) and (8). These values and also the valuesof other constants that have been used in thesecalculations are given in Table 1.References1. KUMAR, K. & NIGAM, P. C., Paper presented at Annual
Convention of Chemists (India), 1977.2. KL:MAR, K., NIGAM, P. C. & PANDEY, G. S., J. phys. cu»;
(in press).3. COO~!BS, L. C., MARGERUM, D. "V. & NIGAM, P. C., Tnorg,
Chem., 9 (1970), 2081.4. COOMBS, L. C. & MARGERUM, D. W., Inorg. Chem., 9 (1970),
1711.5. MARGERUM, D. "V., BYDALEK, T. J. & DISHOP, J. J., J.
Am. chem. Soc., 83 (1961), 1791.6. PAGENKOPF, G. K., J. coord. Chem., 2 (1972), 129.7. DAVIES, T., SINGER, S. S. & STAVELEY, L. A. K., J. chem,
Soc. (Lond.), (1954), 2304.8. CROUSE, "V. C. & MARGERUM, D. W., Inorg, cu-«, 7
(1968), 2239.9. CAULLET, c.. Bull. Soc. cu«, s-: (1963), 688.
S. VIVEKANANDAN, K. VENKATARAO & M. SANTAPPA
Department of Physical Chemistry, University of MadrasGuindy Campus, Madras 600025
and
SP. SHANMUGANATHAN
Department of Chemistry, Pachaiyappa's CollegeMadras 600030
Received 26 April 1978; accepted 23 May 1978
The kinetics of the reaction between mesityl oxideand chloramine-T (CAT) in aqueous sulphuric acidin the presence of KHSO. has been studied. Theresults indicate a radical chain mechanism to beoperative which is quite novel in CAT kinetics.
CHLORAMINE-T (CAT) has estab!ished itselfas an efficient and dependable OXidant and a
versatile chlorinating agent in chemical analysis--'and in reaction kinetics=". Only simple productsha ve been noticed so far in its reaction withsubstratess", We report in this communi~ation .ourkinetic evidence for a novel halogena tive oligo-merization of mesityl oxide (MO) by chloramir.e-Tin aqueous (O'375M) sulphuric acid.. .
In the presence of KHS04, the r~actIO!l manifestsa typical fractional order behaVIOur, i.e. a clean1·5 order in [CAT] and a 0·5 order at low [MO]«O·OI5M) which changes to zero. order . ~md~rpseudo conditions (1 :.15).. Thi~ is. qurte f"!luhar l,nfree radical polymerization kinetics. Beslde~ th:sMichaelis-Menten type of behavic:~r, .the rea.ctIOn ISassociated with very fast equilibria dunng theinitial stages. This kinetic evidence fo~ co.mplexformation is supported by the large shifts m theA values for the reaction mixture when com-p~~~d to those of the reactants. A ne&ligible salteffect (fL: 0·477M to 0'777M; k at 40 : 0·219 to0.2671\,1-0•5 sec+) and a marginal increase in ratewith increasing [H30+] (0·113M to 0'375M; ~ at40°: 0·244 to O·320M-0.5 sec+) have been noticed.This beha viour indicates that the ionic mechanismpostulated in reactions involvir,g. CA16 may r.ot.beoperative under our kinetic conditions. The reactionis considerably faster in the absence of. addedmineral acids suggesting <in altogether differentmechanism. Initially added CI. has a markedinfluence on the rate which could be explained byits oxidation to Cl" that helps fz ster prop, gat ionof the chains. The overall activation energy is64·7 kJ mol! (35-50°; k: 0·254 to O·958M-0.5 see-I).Mass law effect is not observed. Ir.stead, the rateincreases slightly with increasing initially cddedp-toluenesulphonamide (PTS) which is one of the
*Presented as a preliminary report at the All I.ndiaseminar on Oxidation-reduction reactions held at the Univer-sity of Madras, January 1978 and with further resultspresented as a paper at the Chemistry symposium heldat the lIT. Madras, March 1978.
519
INDIAN J. CHEM., VOL. 16A, JUNE 1978
Na CH. H 0
/ '" I "{P-H.C.C,H•.S02}·N : CAT; C=C-C-CH •. MO
. R '" Cl CH: 4 3 2 1 .CHa H 0
"'.. I "C-C-C-CH#: M"
/ ICH, Cl
Rrim: C";
Scheme 1
reaction products (2'5x 10-4M to 1X 10-3M; k at40°: 0·267 to 0·309M-o.5 sec-I). This <gain isin contrast to the rate suppression encountered inreactions wherein ionic mechanism is operatives.
Chlorinated oligomeric material Were found to bethe other reaction product. Further, the reactionshows variable stoichiometry clearly ir.dicatir g thatthe nature of the reaction products markedlydepends on reactant concentratiors, kinetic condi-tions and reaction time? Separate kinetic studiesusing dichloramine-T rule out its involvement in thekinetic scheme under our experimental conditions.Further, induced polymerize tion of acrylonitrileshows the involvement of free radicals in thesystem .. All these experimental facts lead us to aradical chain mechanism (Scheme 1) which is quitenovel in CAT kinetics.CAT+H+ ~ CH+Na+MO(keto)~ MO(enol)
KMO(enol)+CH ~ CM
1<.CM-+C'+M"
•.. (1)•.. (2)
•. .(3)
•.. (4)
•.. (5)
••. (6)
• .. (7)
k,M"+M-+M2
k,.C·+M -+ M'+PTS
fl.M'+M-+M2
•.. (8)
520
k,M~+CH -+ Oligomeric material +C'
k,
... (11)
where[CM]
K = [CATJt[M]t ... (12)
[M], ~ [M], (t = total: f = free)Since the major CAT consuming step is only (9),the first term on the right hand side of (1l) willnot be signifier nt which is in agreement with theobserved order for the reaction.
The present work indicates for the first timethe potentiality of CAT as an initia tor in freeradical polymerization. Further investigations (i) onsuch polymeriz ..tior s, (ii) with other a~-ursa tura tedsystems, and (iii) in different solvent enviror mar.tsare in progress.
One of the authors (S.V.) is grateful to the UGC,New Delhi for a teacher research fellowship.
References1. JENNINGS, V. ]., CRC Crit. Rev. Anal. Chem., 3 (1974),
407.2. SHANMUGANATHAN, SP. & VIVEKANANDAN, S., Indian J .
Chem., 15A (1977), 428.3. MAHADEVAPPA, D. S. & NAIDu, H. M. K., Indian J.
Chem., 14A (1976), 808.4. RADHAKRISHNAMURTHI. P. S. & SAHU, B., Indian J.
Chem., 15A (1977), 700.5. MUSHRAN, S. P., SANEHI, R. & AGRAWAL, M. C., Z.
Naturforsch, 27B (1972), 1161.6. NATARAJAN, M. M. & THIAGARAJAN, V., J. chem. Soc.
Perkin II, (1975), 1590.7. A complete and detailed discussion of the product
analysis and identification under our kinetic and otherdifferent conditions by TLC, GLC and elemental ana-lysis and UV, IR, NMR and mass spectral studiesappears elsewhere.
